Several examples of conventional techniques are shown and disclosed in Japanese Patent Nos. 1980-23621 and 84-86231, as well as Japanese Patent No. 1978-34664, which corresponds to U.S. Pat. No. 3,923,479. For the sake of convenience, these prior art arrangements are basically illustrated and substantially simulated in FIGS. 4-6 of the subject application.
Referring now to FIG. 4, there is shown a standard two-cylinder type of dehumidification unit. A conventional air compressor CO is connected to cooler CL. That is, the outlet of the air compressor CO is coupled to the input of cooler CL. A drain valve DV has its inlet connected to the outlet of the cooler CL. The outlet of the drain valve DV is connected to the inputs of a pair of electromagnetic valves MV1 and MV2. A pair of dehumidification cylinders DR1 and DR2 containing desiccating medium have their inlets connected to the outlets of the electromagnetic valves MV1 and MV2, respectively. A pair of directional control check valves CV1 and CV2 are connected to the respective outlets of the dehumidification cylinders DR1 and DR2. A pair of chokes or throttles NV1 and NV2 are connected in parallel to the respective check valves CV1 and CV2. A regenerating air reservoir SR is connected to the throttles NV1 and NV2 and the check valves CV1 and CV2. A check valve CV3 prevents reverse air flow from an air reservoir MR to the regenerating air reservoir SR. That is, the air reservoir MR is connected to the regenerating air reservoir SR by the check valve CV3. A governor GO is installed in combination with the air reservoir MR and controls the maximum pressure surge to a value of P2 and also controls the minimum pressure surge to a value of P1. Thus, the pressure in the air compressor CO and in the drain valve DV are controlled. The electromagnetic valves MV1 and MV2 each have an exhaust position b which closes the inlet as well as opens the outlet into the atmosphere during off time periods and have a supply position a which allows the air to go from the inlet to the outlet and closes the open exhaust during on time periods.
Now when the electromagnetic valve MV1 is in the supply position a and with the electromagnetic valve MV2 off, the humid air from the air compressor CO is supplied to the dehumidification cylinder DR1 through the cooler CL and the drain valve DV. The humid air is dried by the desiccant medium in the dehumidification cylinder DR1. From there the dried air flows to the regenerating air reservoir SR through the check valve CV1 and reaches the air reservoir MR through the check valve CV3. At this time, a portion of the dried air which came through the check valve CV1 flows to the outlet of the other dehumidification cylinder DR2 through the throttle NV2. There the dried air regenerates the desiccant medium in this dehumidification cylinder DR2 and the air flowing out picks humidity from the dessicant. This humid air is then exhausted through the electromagnetic valve MV2 which is in the exhaust position b.
Now when the process is reversed, namely, the electromagnetic valve MV1 is turned off and the electromagnetic valve MV2 turned on, the humid air from the compressor CO is dried in the other dehumidification cylinder DR2 and at the same time regeneration of the desiccant medium takes place in the dehumidification cylinder DR1.
When the pressure in the air reservoir MR reaches the upper limit pressure surge value P2, the governor GO stops the air compressor CO and simultaneously causes the draining of water in the drain valve DV. When the pressure of the air reservoir MR decreases to the lower limit surge value P1, the governor GO stops the draining of water from the drain valve DV and simultaneously causes the air compressor CO to start up operation.
Referring now to FIGS. 5 and 6, there are shown time charts relating to the control method of switching operations which occur during the dehumidifying and regenerating cycles of the respective cylindrical dehumidifiers DR1 and DR2 of FIG. 4.
In a first type of conventional process shown in FIG. 5, the electromagnetic valves MV1 and MV2 are switched on and off in a fixed normal time T. The time periods T are set by a suitable timer (not shown in the Fig.). Thus, the dehumidifying and regenerating cycles of each of the dehumidification cylinders DR1 and DR2 are reciprocally repeated at equal times T.
In a second type of conventional process shown in FIG. 6, there is shown a time chart which was made from the listing of FIG. 3 which appears in Japanese Patent No. 1978-34664, corresponding to U.S. Pat. No. 3,923,479. It will be seen that the swithing cycles, namely, the on and off periods, are set by the governor GO. The governor Go senses the pressure P of the air reservoir MR, and either causes the operation or the non-operation of the air compressor CO. When the air compressor CO is stopped, both electromagnetic valves MV1 and MV2 are turned off and the condition of both dehumidification cylinders DR1 and DR2 is set for regeneration. When the air compressor CO is restarted, the condition of the previous operating period is reversed and the electromagnetic valves MV1 and MV2 are switched on. Thus, the regenerating and dehumidifying of the dehumidification cylinders DR1 and DR2 are reversed.
The present invention attempts to solve the following problems. In the first conventional process shown in FIG. 5, the dehumidifying and regenerating cycles in the dehumidification cylinders DR1 and DR2 are reciprocally repeated every time period T as set by a timer without any relationship to the operation and non-operation phases of the air compressor CO. Even when the air compressor CO is stopped, the cycling or frequency of switching is continuous, thereby increasing wear and tear and extending the useful life of the electromagnetic valves MV1 and MV2. In such a continuous switching system, the control parts are susceptible to undue failures.
In the second conventional process shown in FIG. 6, the following problem is normally present.
First in the case, air is introduced into the air reservoir MR from the atmosphere until the upper limit surge value P2 of the governor GO t 10 in FIG. 6 is reached. In this case the pressure increase from the lower limit surge value P1 to the upper limit surge value P2 is slow t 11 in FIG. 6 because of the large consumption of air in the air reservoir MR during introduction of air from the governor GO. Thus, the driving operation is continued by the same dehumidification cylinder DR1 during the entire time, and thus the drying limit is surpassed and the efficiency of drying quickly decreases.